The 3rd generation partnership project (3GPP) long term evolution (LTE) is an evolving high speed, high capacity standard for user equipment (UE) emerging as a globally accepted standard. The LTE that is being deployed globally operates in packet switched (PS) domain. Currently, UEs equipped with LTE technology utilize LTE PS domain to handle data traffic while the voice traffic is handled by legacy circuit switched (CS) networks (legacy radio access technologies (RATs)), such as a global system for mobile communications (GSM), a universal mobile terrestrial system (UMTS) and a GSM enhanced data for global evolution (EDGE) radio access network (GERAN). To support CS domain communication, such as voice calls, the UE in LTE has to switch to CS supporting legacy RATs.
The circuit switched fall back (CSFB) procedure standardized by 3GPP technical specification enables the UE's to perform this switching during mobile originated (MO) or mobile terminated call (MT). The 3GPP standard defines inter-RAT (I-RAT) for mobility (switching) between LTE and earlier 3GPP technologies, such as UMTS and GERAN. To acquire a legacy RAT during I-RAT switching the 3GPP standard provides redirection based CSFB procedure.
In accordance with existing 3GPP standard for redirection based CSFB procedure, when the CS call is attempted while UE is in LTE, the UE starts an extended service request (ESR) procedure. When the extended service request is received by e-UMTS terrestrial RAN (UTRAN) Node B (eNB) of the LTE network, the eNB provides the UE with radio resource control (RRC) connection release along with redirection request including the target RAT frequency on to which the UE can camp for CS call. However, at many instances, redirection from LTE to other RATs like UMTS and GERAN fails due to redirected frequency being in poor signal conditions. The existing redirection based CSFB procedure fails to determine for and utilize other available frequencies which are comparatively better and on which the UE can camp to setup new RRC connection for MO call.
Moreover, in accordance with the existing redirection based CSFB procedure once the RRC connection is initiated, the UE camps to the serving frequency until the expiry of timer specified by T300*N300 even though the UE detects poor signal conditions. This timer in the existing CSFB procedure restricts the number of attempts to retransmit RRC connection request within the preset ESR timer. Thus, existing methods increase the CSFB call failure rate.
Therefore, a need exists for a method and a system to provide improved CSFB procedure to effectively reduce the CSFB call failure rate.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.